CA2199211A1 - Method and apparatus for wash, resuspension, recollection and localization of magnetizable particles in assays using magnetic separation technology - Google Patents

Abstract

Method and apparatus for enabling resuspension wash and magnetic localization of sample components bound to particles with magnetic properties in reaction vessels during separation and wash for enhanced chemiluminescent signal generation in biomedical assays. The assays involve moving reaction vessels past magnetic arrays that partially localized the particles prior to passing a gap where washing occurs, with or without resuspension, after separating out the unbound particles and liquid. The band of particles is further localized by a focusing magnet at the end of the array prior to dosing the vessel with acid for chemiluminescent purposes. A block of soft magnetic material is employed in place of a magnet in the gap to minimize magnetic strength at the gap. Trimmed magnets adjacent the gap cause left, then right, particle shifting that localizes the magnetizable particles. The gap enables improved resuspension by wash, whereas the localized particles enable more efficient resuspension by reagent.

Description

21992~1 FI~T.n OF T~F. INV~NTION

2 The invention generally relates to the field of 3 biomedical assays employing magnetic separation 4 techniques, and specifically to a method and apparatus for focusing or localizing magnetizable particles during 6 separation and wash in such assays.

8 RZ~CKGROT~n OF T~F. INVF.~TION
9 Heterogeneou~ immunoassays typically require the separation of sought-for components bound to component-11 selective particles from unbound or free components of the 12 assay. To increase the efficiency of this separation, 13 many assays wash the solid phase (the bound component) of 14 the assay after the initial separation (the removal or aspiration of the liquid phase). Some chemiluminescent 16 immunoassays use magnetic separation to remove the unbound 17 assay components from the reaction vessel prior to 18 addition of a reagent used in producing chemiluminescence 19 or the detectable signal indicative of the amount of bound component present. This is accomplished by using 21 magnetizable particles including, but not restricted to, 22 paramagnetic particles, superparamagnetic particles, 23 ferromagnetic particles and ferrimagnetic particles.

~9~1~
1 Tested-for assay components are bound to component-2 specific cites on magnetizable particles during the course 3 of the assay. The associated magnetizable particles are 4 attracted to magnets for retention in the reaction vessel while the liquid phase, containing unbound components, is 6 aspirated from the reaction vessel.
7 Washing of the solid phase after the initial 8 separation is accomplished by dispensing and then 9 aspirating a wash buffer while the magnetizable particles are attracted to the magnet.
11 Greater efficiency in washing is accomplished by 12 moving the reaction vessels along a magnet array having a 13 gap in the array structure proximate a wash position, 14 allowing the magnetizable particles to resuspend during the dispense of the wash bu~fer. This is known as 16 resuspension wash. Subsequent positions in the array 17 include magnets, allowing the magnetizable particles to 18 recollect prior to aspiration of the wash buffer and 19 introduction of reagent beyond the end of the magnet array.
21 One prior art wash block configuration provides an 22 aluminum insert in the gap of the magnet array at the wash 23 position. Rather than simply removing a magnet from the 1 resuspension position, the insert prevents a reaction 2 vessel from becoming misaligned and jammed in the magnet 3 array. While functioning adequately for assays which 4 employ resuspension wash, it is evident that the provision of an aluminum insert in place of a magnet at the wash 6 position adversely effects assays which do not use the 7 resuspension in washing but which proceed through the wash 8 position without resuspension. A single band of g magnetizable particles which is normally formed along the interior of the reaction vessel as it passes the magnet 11 array, during the initial separation, is split into two 12 smaller bands on either side of the reaction vessel due to 13 attraction by the magnets on either side of the insert at 14 the resuspension and wash position. Since the reagent is introduced into the reaction vessel in a stream directed 16 toward where the magnetizable particles collected before 17 splitting, the split in the banding of the magnetizable 18 particles results in the stream missing the main 19 concentration of magnetizable particles. Poor resuspension of the magnetizable particles during 21 resuspension wash and upon addition of an acid reagent 22 used to condition the bound component reagent in the 23 generation of a chemiluminescent signal results.

,~
1 Therefore, the prior art fails to provide a wash 2 region which enables the efficient washing of magnetizable 3 particles during the wash phase of a magnetic separation 4 assay without adversely effecting a~says not employing resuspension wash.

7 SUMM~Y OF T~ I~VF~TION
8 It is an object of the present invention to provide 9 methods and apparatus for focusing or localizing magnetizable particles during separation and wash for 11 enhanced signal generation in assays which use magnetic 12 separation technology. It is a further object of the 13 pre~ent invention to provide a wash region enabling 14 enhanced suspension of solid phase components for a sample, regardless of whether it undergoes resuspension 16 wash.
17 These objects are achieved by employing an insert of 18 soft magnetic material in place of separation magnets at a 19 wash position in the array, wherein the insert has a width greater than the width of a reaction vessel passing 21 thereby. Further, the magnets of the array both up and 22 downstream of the wash position terminate at locations 23 intermediate the reaction vessel for enhanced focusing of 219~211 1 magnetizable particles in the path of a reagent stream, 2 resulting in improved resuspension of the magnetizable 3 particles by the reagent. Therefore, resuspension wash 4 efficiency is enhanced, and magnetizable particle focusing is increased, leading to a more efficient magnetizable 6 particle resuspension for the signal generation portion of 7 the assay.
8 At the end of the magnet array, a ~ocusing magnet g having a face dimension less than a vessel width is employed in the array to more completely localize the 11 magnetizable particles prior to being in the path o~ an 12 injected acid stream employed to initiate the reaction 13 leading to chemiluminescence.
14 For assays not employing resuspension wash, the provision of the soft magnetic insert results in avoidance 16 of split banding of the magnetizable particles, while 17 magnetizable particle focusing results in improved 18 chemiluminescent reaction.
19 For assays employing resuspension wash, the soft magnetic insert enables resuspension wash while avoiding 21 premature collection and splitting of magnetizable 22 particles due to the influence of magnets adjacent to the 23 wash position. As with assays not employing resuspension ~, 21g92~
1 wash, magnetizable particle focusing results in improved 2 chemiluminescent reaction.

4 RRIEF DF..~CRIPTION OF ~E ~RAWIN~S
This invention is pointed out with particularity in 6 the appended claims. The above and further advantages may 7 be more fully understood by referring to the following 8 description and accompanying drawings of which:
9 Fig. lA is an elevation view of a magnet array and a sequence of reaction vessels passing therethrough 11 according to the present invention;
12 Fig. lB is an elevation view of the magnet array of 13 Fig. lA in which resuspension wash is performed;
14 Fig. 2 is an elevation view of the magnet array of Fig. lA illustrating a reaction vessel transport 16 mechanism;
17 Fig. 3 is a rear elevation view of the magnet array 18 of Fig. lA illustrating a magnet array support structure;
19 Fig. 4A is a side elevation view of a non-resuspension wash nozzle oriented proximate a reaction 21 vessel for use in the magnet array of Fig. lA; and - ~ 219921~
1 Fig. 4B is a side elevation view of a resuspension 2 wash nozzle oriented proximate a reaction vessel for use 3 in the magnet array o~ Fig. lB.

DFlTAITl~ln D~C~IPTION
6 To increase the efficiency of the separation of bound 7 components from free components in immunoassays, many 8 assays wash the solid phase (bound component) of the assay 9 after the initial separation (removal of the liquid phase and unbound component). The present invention operates in 11 the context of a chemiluminescent immunoassay of known 12 type which uses magnetic separation to remove unbound 13 assay components from a reaction vessel such as a cuvette.
14 The presently disclosed method and apparatus enables a resuspension wash of magnetizable particles with 16 improved wash efficiency and focuses magnetizable 17 particles from a band to a small region or dot, enabling a 18 more efficient resuspension of magnetizable particles for 19 a signal generation portion of the assay.
In all of the following discussions, it is assumed 21 that the reaction vessels progress from the left-hand side 22 of the illustrations to the right-hand side past a fixed 23 magnet array at regularly timed intervals, although ~ 21~92~
1 continuous motion i8 not excluded. Means for imparting 2 lateral translation of the reaction vessels is described 3 subsequently with regard to Fig. 2. In an exemplary 4 embodiment, such interval is approximately 15 seconds.
Additionally, throughout this description, aspiration and 6 dispense functions are executed via means known in the art 7 without full details being shown.
8 The magnet array of Figs. lA and lB includes a 9 succession of reaction vessels such as cuvettes 12, each containing assay components and magnetizable particles 14 11 which are initially in a freely distributed state within 12 the respective cuvette 12. The concentration of solid 13 phase (bound component) of the assay rem~ln;ng in free 14 suspension in the cuvette at position B is less than that of the first cuvette 12 in position A due to the initial 16 collection of solid phase proximate magnets of the array 17 16 at position B. In the cuvette 12 of position C, this 18 effect is more evident. By the time a cuvette has 19 progressed to position D, the majority of the solid phase 14 has collected proximate respective magnets of the array 21 16.
22 References to "magnets" adjacent a respective 23 position are understood to refer to a pair of adjacent ~ 2199211 1 magnets of oppositely oriented polarity, one above the 2 other, proximate the respective cuvette position. A band 3 of magnetizable particles 14 forms along the junction of 4 these two magnets, where the magnetic gradient is at a maximum.
6 Non-resuspension washes are provided at positions F, 7 G, and M in the illustrative embodiment of Fig. lA, and at 8 positions F and M in the embodiment of Fig. lB. At these 9 positions, liquid phase is aspirated from the cuvette 12 via tubes (15, 17, 19 in Fig. lA and 15, 19 in Fig. lB) 11 and wash buffer is reintroduced via nozzles (30, 32, 34 in 12 Fig. lA and 30, 34 in Fig. lB). The nozzles are 13 positioned in front of respective tubes in the view of 14 Figs. lA and lB. In particular, the nozzles are angled toward the front of the respective cuvette 12 (out of the 16 page in Figs. lA and lB) to avoid disturbing the pellet of 17 solid phase 14 collected at the respective magnets of the 18 array 16.
19 The tube 21 at position N of Figs. lA and lB is employed to aspirate liquid phase from the respective 21 cuvette 12 prior to the introduction, at position P, of 22 reagent via nozzle 36, the reagent facilitating a 23 subsequent chemiluminescent reaction within a luminometer.

2199~1~
1 In contrast to the non-resuspension wash nozzles (30, 32, 2 34 in Fig. lA and 30, 34 in Fig. lB), the reagent 3 dispensing nozzles 36 are angled toward the pellet of 4 solid phase 14 in order to thoroughly disperse it.
In prior art magnet arrays, a portion of the liquid 6 phase may remain trapped within the solid phase 14 prior 7 to introduction of the reagent at position P, even after 8 repeated non-resuspension washes, such as at positions F, 9 G, and M in Fig. lA and positions F and M in Fig. lB.
This trapped liquid phase limits the accuracy of the 11 assay.
12 At position K of Fig. lA, the magnets of the array 16 13 proximate the cuvettes 12 are disposed at a lower 14 position. This provides the solid phase pellet 14 with time to recollect at the lower position prior to the 16 introduction of assay reagent at position P. Thus, when 17 reagent is directed at the pellet 14 in position P by the 18 nozzle 36, the solid phase 14 will be centrally located in 19 the reaction vessel 12 when the acid is applied at position P. However, such repositioning of the pellet 21 does not necessarily enhance the ability o~ the non-22 resuspension washes to rid the solid phase 14 of trapped 23 liquid phase.

219921~
1 In Fig. lA, a resuspension wash is not employed, and 2 as such the focused, or localized, solid phase remains 3 proximate respective magnets 16 as the cuvette 12 4 progresses through the wash block.
In contrast, the magnet array of Fig. lB does employ 6 a resuspension wash. Resuspension washing of the solid 7 phase involves the aspiration of the liquid phase 8 containing the unbound components of the assay from the 9 cuvette 12 at position G via the tube 17 while the bound components are held in place by respective magnets in the 11 array 16. This is followed by re-introduction of wash 12 buffer into the cuvette 12 at position H by a dispense 13 nozzle 32 angled at the solid phase pellet 14 collected at 14 the back of the cuvette 12 proximate the magnets 16.
At position H, magnets of the array 16 have been 16 replaced by a soft magnetic insert 20. By dispensing wash 17 buffer onto the magnetizable particles via the nozzle 32 18 in the absence of magnets in the array 16, the 19 magnetizable particles are resuspended, exposing more surface area, and freeing liquid phase trapped during 21 initial magnetizable particle collection. A~ter the solid 22 phase has been resuspended, it is recollected by a 23 subsequent series of magnets in the array 16 at positions ~ 2i~9211 1 I et ~eq. prior to aspiration of the wash buffer and 2 introduction of the acid reagent at position P. Other 3 wash stages, in addition to those illustrated, are 4 possible.
The wash block o~ Figs. lA and lB is provided with a 6 large gap in the magnet array at position H, thus 7 enhancing resuspension wash. Prior art magnet arrays 8 employed narrower gaps, resulting in split bands of 9 magnetizable particles due to the attractive forces of array magnets on either side of the narrow gap.
11 The present invention avoids the splitting of the 12 solid phase material into bands at opposite sides of the 13 cuvette 12, in part, by providing a focusing of the solid 14 phase 14 into a smaller band or dot 24. The gap at the resuspension wash position is filled with an insert 20 16 made of a soft magnetic material such as low carbon steel.
17 Further, the magnets of the array 16 at positions G and I
18 on either side of the resuspension wash position, position 19 H, are trimmed such that the gap in the array of magnets 16 and the insert 20 extend proximate a region of the 21 reaction vessels 12 previously occupied by the solid phase 22 band 14 adjacent to the resuspension wash position.

1 As a result, magnetizable particles linearly banded 2 by the magnets in the previous positions, but which are no 3 longer directly aligned with magnets of the array 16, 4 migrate along the reaction vessel 12 walls towards portions of the reaction vessel interior proximate the 6 trimmed magnets 16. For instance, in po~qition G, the 7 magnets 16 are trimmed on the right-hand side.
8 Magnetizable particles formerly aligned in the trimmed 9 region now migrate to the center of the vessel 12, over the trimmed magnets 16.
11 The magnetizable particle banding pattern in the 12 reaction vessel at the resuspension wash position, 13 position H, rem~; n-q unchanged in the absence of 14 resuspension wash (Fig. lA). With resuspension wash (Fig.
lB), the large soft magnetic insert 20 enables the 16 complete resuspension of the solid phase 14 free of 17 influence of magnets at positions G and I. Also, the 18 provision of magnets trimmed on a left-hand side at 19 position I downstream of the resuspension wash position, position H, further serves to avoid influencing the 21 magnetizable particles during the resuspension wash in 22 Fig. lB.

1 The array 16 magnets at position I, downstream of the 2 resuspension wash position, position H, and the soft 3 magnetic insert 20, is also trimmed on its left-hand side 4 in Fig. lA. This serves to focus the solid phase 14 downstream of the resuspension wash position, position H.
6 The magnetizable particles on the left side of the 7 reaction vessel 12 are no longer directly aligned with 8 magnets 16 at position I. Rather, they migrate toward the 9 right, into the center of the vessel 12. The net effect is a conversion of the magnetizable particles from a wide 11 band 14 to a more compact, centrally located band 26.
12 For the embodiment of Fig. lA, the single 13 magnetizable particle band at position H does not split 14 into two bands as in the prior art because the soft magnetic insert 20 acts to short out, or minimize, the 16 magnitude of the field gradient in the resuspension wash 17 position, position H, and because trimming the magnets of 18 the array 16 at positions G and I reduces the reach of the 19 fields, from the same, into the resuspension position H.
At position M, trimmed magnets 27 are provided to 21 further narrow the band of collected magnetizable 22 particles. In a further embodiment, even smaller magnets 23 28, focusing magnets, are employed at position N to focus 2~99211 1 the magnetizable particles into yet a smaller area, thus 2 providing a smaller target of solid phase 24 at position P
3 for more efficient resuspension upon dispense of reagent.
4 Smaller, focusing magnets 28 are not used in a preferred embodiment for the initial collection of the solid phase 6 because, amongst other things, the larger the magnet 7 surface area, the faster the collection of the 8 magnetizable particles.
9 In an alternative embodiment, all of the magnets in the array 16 along the length of the wash block are 11 provided as focusing magnets 28, though the resuspension 12 wash position, position H, would continue to be provided 13 with a gap such as that provided by the soft magnetic 14 block 20 of Figs. lA and lB. However, such an embodiment would require more time for each reaction vessel 12 to be 16 proximate the magnets 28 in the array to provide an 17 equivalent degree of capture capability due to the smaller 18 size of the magnets in such an embodiment.
19 In yet another embodiment of the present invention, it is possible to enable further focusing of the 21 magnetizable particles by employing another gap in the 22 magnet array 16 prior to the focusing magnets 28 at 23 position N. For instance, such a gap could be employed at ~99~11 1 position L. Here, the magnetizable particles 14 have 2 already been gathered at an interior wall o~ the reaction 3 vessel 12. A gap at position L would allow the 4 magnetizable particles to become released from the interior wall, though they would generally remain 6 localized. Thus, re-attraction by subsequent focusing 7 magnets 38 would not take an excessive amount of time.
8 Illustratively, in a first embodiment illustrated in g Fig. 2, the reaction vessels 12 containing the suspended solid phase 14 are laterally translated along the magnet 11 array 16 by a linked conveyor belt 40 comprised of a 12 sequence of reaction vessel receptacles 42. A sequence of 13 freely rotatable rollers 44 are employed to provide 14 support for the conveyor belt 40. At least one such roller 46 is mechanically connected to a motor 48, wherein 16 the motor 48 rotates this roller 46, which in turn causes 17 the conveyor belt 40 and the reaction vessels 12 disposed 18 therein to translate relative to the magnet array 16.
19 The rear view of the magnet array in Fig. 3 illustrates a first embodiment of a magnet array 16 21 support structure 50. The magnet array 16 of Fig. 3 is a 22 reverse view of the magnet array 16 of Figs. lA and lB.
23 The magnets of the array are backed by a conductive -2 1 ~

1 material such as high-iron, low-carbon steel to focus the 2 magnetic field toward the reaction vessels 12. The 3 support structure 50, which attaches to the magnet backing 4 material, is preferably provided from a magnetically non-reactive material such as aluminum or one of its alloys to 6 avoid unwanted disturbances in the magnetic field 7 established within the reaction vessels. The magnets of 8 the array 16 and the backing material are fastened to the 9 support structure 50 in a variety of ways, including via the use of adhesive or mechanical fasteners. The support 11 structure 50 is itself suspended by being mechanically 12 attached to a wall of an enclosure (not illustrated), 13 either by adhesive, mechanical fasteners, or some 14 combination thereof.
In the illustrated embodiment of the support 16 structure in Fig. 3, the element is segmented into three 17 portions: an initial portion to ~he right of Fig. 3, a 18 central portion, and a small final portion on the left.
19 The latter provides support for the focusing magnets 24.
In an alternative embodiment, the central portion and the 21 final portion are combined, such that the support 22 structure is formed of two portions.

1 Fig. 3 also illustrates a rear view of the soft 2 magnetic insert 20. Disposed in a central location 3 thereof is a cross-section of a mechanical fastener 52 4 such as a screw employed in securing the insert 20 to a wall of the enclosure. In alternative embodiments, the 6 soft magnetic insert is supported by a respective support 7 element such as a stanchion or by an extension of the 8 array magnet support element 50. In the latter 9 alternative, the support element 50 would then be one continuous element, if the final portion and the central 11 portion are continuous, or two elements if the focusing 12 magnets 24 is supported independently.
13 The orientation of wash buffer nozzles as employed 14 along the magnet array 16 of the foregoing is illustrated in Figs. 4A and 4B. In particular, a nozzle 30 such as 16 that used for reintroduction of wash buffer at position F
17 in Figs. lA or lB is shown in cross-section in Fig. 4A.
18 Solid phase 14 has collected proximate the magnet array 16 19 (supported by the support element 50) at the rear of the reaction vessel 12. The nozzle 30 is oriented with 21 respect to the reaction vessel 12 to provide a stream 60 22 of wash buffer from a wash buffer reservoir 62 via a pump 23 64 to a front, interior surface of the reaction vessel 12.

~ 21g92~1 1 Thi~ avoid~ disturbing the solid phase collected at the 2 rear o~ the vessel 12.
3 In Fig. 4B, the orientation o~ a nozzle 32 such as 4 that used for resuspension wash at position H in Fig. lB
is illustrated in Fig. 4B. A stream 66 of wa~h buffer 6 from the re~ervoir 62 via the pump 64 is directed at the 7 solid pha~e previously collected proximate magnets in the 8 array 16, but now adjacent the soft magnetic insert 20.
9 The solid phase is there~ore not retained by magnets, and is easily washed back into suspension by the stream 66 of 11 wash buffer from the nozzle 32.
12 Having described preferred embodiments of the 13 invention, it will be apparent to those skilled in the art 14 that other embodiments incorporating the concepts may be used.
16 For instance, though the present invention has been 17 described in the context of a chemiluminescent 18 immunoassay, it can be applied to other assay environments 19 in which the separation of bound and unbound components by magnetic separation is required. Further, the exact 21 number of positions in which magnetizable particles are 22 exposed to magnets 16 depends upon the exact nature of the 23 desired separation, the configuration of the magnets 16, 219~21~
1 the characteristics of the magnetizable particles and the 2 associated bound component, etc.
3 Nozzle 32 has been shown in two locations in Figs. lA
4 and lB, specifically position H in Fig. lA and position I
in Fig. lB. While provided as one nozzle with a like 6 reference identifier in both figures, each embodiment of 7 Fig. lA and lB could be provided with a nozzle at posltion 8 G for non-resuspension wash, and another nozzle at 9 position H for use in an embodiment employing resuspension wash. Thus, the same array configuration could be used 11 for assays both employing and not employing resuspension 12 wash.
13 In addition to the illustrated embodiment of Fig. 2, 14 other means for translating the conveyor belt are envisioned, such as a friction drive disposed on either 16 side of the conveyor at one or more positions.
17 In yet another embodiment of the present invention, 18 the reaction vessels 12 are translated along the magnet 19 array 16 by way of a sequence of respective reaction vessel yokes (not illustrated) connected to the respective 21 reaction vessel near the top of the vessel.
22 The arrangement of elements in Figs. 4A and 4B is a 23 generalized illustration of the relationship between the 1 elements, and is not intended to represent a preferred 2 layout. For instance, the nozzle 30, 32 in Figs. 4A and 3 4B can also be located at the same relative position above 4 a respective reaction vessel 12, but angled in opposite directions to properly direct the respective stream 60, 6 66. Further, the pump and reservoir can be provided in a 7 varie~y of ways, as known to one skilled in the art.
8 These and other examples of the invention illustrated 9 above are intended by way of example and the actual scope of the invention is to be determined from the following 11 claims.

Claims (22)

1. A system for clustering sample particles bound to molecules with magnetic properties in reaction vessels within an assay instrument, the system comprising:
a magnet array providing plural stations past which said reaction vessels transit in sequence, said plural stations comprising one or more first stations at which said magnet array provides a magnetic field which causes vertical clustering of said bound particles in a vessel as said vessels transit said magnet array;
one or more second stations at which said magnet array provides a magnetic field which causes horizontal clustering of said bound particles in a vessel as said vessels transit said magnet array.

2. The system according to claim 1, wherein said magnet array at said one or more second stations directs said magnetic field to slide said bound particles in one horizontal direction at a first one of said one or more second stations, and in an opposite horizontal direction at a further one of said one or more second stations.

3. The system according to claim 1, wherein said magnet array at said one or more second stations provides a narrowed magnetic field to cause said clustering.

4. The system according to claim 1, wherein said magnet array includes a plurality of said one or more first stations surrounding a plurality of said one or more second stations, wherein said magnetic field is directed to slide said bound particles in one horizontal direction by a first one of said one or more second stations, and in an opposite horizontal direction by a further one of said one or more second stations.

5. The system according to claim 4, further including at least one further second station beyond said one or more first stations, said at least one further second station providing a narrowed magnetic field to cause said clustering.

6. A wash block in a magnet array providing magnetic separation of bound and unbound components in reaction vessels moving past said wash block in an assay instrument, said wash block comprising:
a resuspension wash region having plural reaction vessel positions as said vessels move past said array, said wash block at resuspension wash region including a central reaction vessel position proximate which said wash block has a soft magnetic insert in said magnet array, a first reaction vessel position disposed before said central reaction vessel position, said wash block at said first reaction vessel position having trimmed magnets and a first portion of said soft magnetic insert proximate one of said vessels, and a second reaction vessel position disposed after said central reaction vessel position, said wash block at said second reaction vessel position having trimmed magnets and a second portion of said soft magnetic insert proximate one of said vessels.

7. The wash block according to claim 6, further comprising:
an initial separation region having plural reaction vessel initial separation positions as said vessels move past said array, said initial separation region disposed before said resuspension wash region, each of said initial separation positions providing magnets proximate a respective reaction vessel.

8. The wash block according to claim 7, further comprising:
a subsequent separation region having plural reaction vessel subsequent separation positions as said vessels move past said array, said subsequent separation region disposed after said resuspension wash region, each of said subsequent separation positions providing magnets proximate a respective vessel.

9. The wash block according to claim 8, wherein at least one of said plurality of reaction vessel subsequent separation positions further comprises at least one focusing magnet pair of size smaller than said magnets provided proximate said reaction vessel initial separation positions.

10. A magnet array for enabling magnetic separation of bound and unbound components in at least one reaction vessel passing therethrough, said magnet array comprising:
an initial separation stage for separating said bound component from said unbound component in said at least one reaction vessel;
a resuspension wash stage subsequent to said initial separation stage, said resuspension wash stage selectively enabling a resuspension wash of said bound component in said at least one reaction vessel;
a succeeding separation stage subsequent to said resuspension wash stage for focusing said bound component within said at least one reaction vessel and for aspirating said unbound component from within said at least one reaction vessel; and a reagent mix stage subsequent to said succeeding separation stage, said reagent mix stage enabling dispensation of a reagent for resuspension of said bound component in said at least one reaction vessel, wherein said initial separation stage, said resuspension wash stage, said succeeding separation stage, and said reagent mix stage collectively comprise plural consecutively arranged reaction vessel positions within said magnet array, and wherein said resuspension wash stage maintains a bound component physical configuration in said at least one reaction vessel in the absence of said selectively enabled resuspension wash.

11. The magnet array according to claim 10, wherein said initial separation stage, said resuspension wash stage and said succeeding separation stage each comprises at least one magnet pair of said magnet array proximate respective ones of said reaction vessel positions.

12. The magnet array according to claim 11, wherein said resuspension wash stage further comprises a wash buffer dispense position having a wash buffer dispense nozzle, wherein said at least one reaction vessel is positioned at said wash buffer dispense position to receive a wash buffer from said wash buffer dispense nozzle.

13. The magnet array according to claim 12, wherein said resuspension wash stage further comprises a soft magnetic insert at said wash buffer dispense position.

14. The magnet array according to claim 13, wherein said resuspension wash stage further comprises a pre-wash reaction vessel position before and a post-wash reaction vessel position after said wash buffer dispense position, wherein said soft magnetic insert overlaps said pre-wash and post-wash positions, and wherein said pre-wash and post-wash positions have respective magnets trimmed to accommodate said overlapping soft magnetic insert.

15. The magnet array according to claim 13, wherein said soft magnetic insert is formed of low carbon steel.

16. The magnet array according to claim 11, wherein said succeeding separation stage further comprises at least one magnet pair, proximate a respective one of said reaction vessel positions, having a size smaller than said at least one magnet pair of said initial separation stage to provide a focusing of said bound components within said at least one reaction vessel at said respective one of said reaction vessel positions.

17. The magnet array according to claim 10, further comprising a secondary resuspension wash stage, disposed consecutively with and between said succeeding separation stage and said reagent mix stage.

18. A method for separating components of an assay, bound to magnetizable particles, from unbound components using a magnet array, said method comprising the steps of:
providing said bound and unbound assay components in a reaction vessel;
passing said reaction vessel proximate a first series of sequentially disposed magnet pairs in said magnet array to induce initial separation of said bound components from said unbound components;
passing said reaction vessel proximate a resuspension wash stage of said magnet array partially comprised of a soft magnetic insert to selectively enable resuspension wash of said bound components; and passing said reaction vessel proximate a second series of sequentially disposed magnet pairs in said magnet array to induce subsequent separation of said bound components.

19. The method according to claim 18, wherein said step of passing said reaction vessel proximate a resuspension wash stage further comprises:
passing, in sequence, said reaction vessel through a first position having a first trimmed magnet pair and a first portion of said soft magnetic insert proximate thereto, a second position having a second portion of said soft magnetic insert proximate thereto, and a third position having a third portion of said soft magnetic insert and a second trimmed magnet pair proximate thereto.

20. The method according to claim 19, wherein said step of passing said reaction vessel proximate a resuspension wash stage further comprises:
aspirating said unbound component from said reaction vessel at said first position; and dispensing a wash buffer into said reaction vessel at said second position.

21. The method according to claim 18, wherein said step of passing said reaction vessel proximate a second series of sequentially disposed magnet pairs further comprises:
passing said reaction vessel proximate a second series of magnet pairs of which a subset of at least one last magnet pair in said second series comprises at least one focusing magnet pair of smaller size relative to other magnet pairs in said second series.

22. The method according to claim 21, further comprising the step of:
aspirating said unbound components from said reaction vessel when said reaction vessel is proximate a last one of said at least one focusing magnet pair; and passing said reaction vessel proximate a reagent mix stage sequentially disposed after said second series of sequentially disposed magnet pairs in said magnet array, wherein a reagent buffer is dispensed into said reaction vessel for resuspending said bound components.